Non-volatile data storage devices, such as universal serial bus (USB) flash memory devices or removable storage cards, have allowed for increased portability of data and software applications. Flash memory devices can enhance data storage density by storing multiple bits in each flash memory cell. For example, Multi-Level Cell (MLC) flash memory devices provide increased storage density by storing 3 bits per cell, 4 bits per cell, or more.
Determining a reading voltage between an Erase (Er) state and an A state of a memory is different than determining the reading voltages between other states. The tail of the cell voltage distribution (CVD) of the Erase state is different from the tails of other states. Because most of the distribution of the Erase state is in negative voltage, and since typical flash memory systems do not have negative sensing capabilities, the erase state may be only partially detectable. Inaccurate determination of the reading voltage of the Er→A border may limit the lifetime of the flash memory.